A wide variety of catalysts have been described for the polymerization of alkylene oxides to produce high molecular weight polymers. Metal-based catalysts are the most common ones. Examples include oxides and/or hydroxides of iron, magnesium, aluminum, and zinc, ammonia-modified amides of calcium, and bimetallic cyanides of zinc and cobalt. Most of these catalysts suffer from several disadvantages including limited molecular weight, inadequate molecular weight control, undesirable coloration and odor of the final polymer, difficulties in removing the catalyst residue from the final polymer, toxic catalyst residue, and product instability.
Aluminum-based catalysts have been known and used for many years.
U.S. Pat. No. 3,135,705 describes a family of catalysts based on alkylaluminum-water, or alkylaluminum-water-bifunctional chelating agent, where one of the functionalities of the chelating agent is OH or SH, and the other contains O, N, or S. Unfortunately, the examples of the patent show that the reaction times with the disclosed catalyst are very long.
U.S. Pat. No. 3,459,688 reports improvements of a catalyst consisting of organoaluminum, a metal salt of a beta-diketone, and water in the presence of an ether compound. Unfortunately, the efficiency of the described catalyst is not sufficient for many applications.
Chemicals Abstracts Vol. 72, 1970, Abstract No. 133374h, abstracting Japanese patent application 70 05,786, proposes a binary catalyst system comprising an organoaluminum and an alpha-amino acid N-carboxy anhydride.
The published Japanese patent application JP 57008223 describes the use of porphyrino-organoaluminum complexes as catalysts for homo- and copolymerization of alkylene oxides. However, S. Inoue, T. Aida, H. Sugimoto, C. Kawamura, and M. Kuroki report in Macromol. Symp. 1994, 88,117-122; and M. R. Mason, and A. M. Perkins report in J. Organometallic Chem. 2000, 599,200-207) that these types of catalysts, even in the presence of polymerization enhancers, are slow, and yield low molecular weight, colored materials.
U.S. Pat. No. 4,376,723 describes a catalyst composition comprised of an alkyl aluminum, a secondary amine, a beta-diketone, and water. The secondary amine could function as a molecular weight adjuster. Unfortunately, high temperatures are required which might not be compatible with low molecular weight alkylene oxides.
U.S. Pat. No. 4,721,817 describes catalysts prepared by contacting phosphorous containing acids with aluminum alcoholates or phenolates, to generate non-ionic surfactants. The molecular weights of the described final products are low.
U.S. Pat. No. 4,933,502 describes catalysts formed by contacting a sulfur-containing acid with alkyl alcoholates or aluminum phenolates. The sulfur atoms in the sulfur-containing components in this patent are hexavalent and are used for the preparation of ethoxylated surfactants.
Kuran, W. et al. (J. Macromol. Sci., Pure Appl. Chem. 1998, A35(3), 427-437) report the preparation of (25,27-dimethoxy-p-tert-butylcalix[4]arene-26,28-diolato)aluminum chloride, and its successful use for the homopolymerization of propylene oxide or cyclohexene oxide. The catalyst activity is low and reaction times of weeks are required to obtain low molecular weight homopolymers.
Antelmann et al. describe in Macromolecules Vol. 34, pp. 3159-3175 (2001) a catalyst system for the polymerization of propylene oxide based on a bridged bis(phenolate) ligand attached to two aluminum centers, in which the bridge is an alkylidene group. Unfortunately, such complexes have an insufficient activity in the polymerization of ethylene oxide.
In view of the above-mentioned deficiencies of the known catalysts for the polymerization of alkylene oxides, it is still desirable to find new compounds which are useful as catalysts in the polymerization of alkylene oxides.